Integrated circuits are still raising the degree of integration; in the manufacture of semiconductor tips such as VLSI's, ultra-fine patterns comprising line widths of not more than a quarter micron must be processed. As one of the means to reduce the pattern dimensions, the use of an exposure energy source emitting a short wavelength radiation for the pattern formation is well known. The merit of shorter wavelength exposures can be understood by the Rayleigh's equation relating the resolution (line width) of an optical system to the wavelength of light.R=k·λ/NAin which λ represents the wavelength of the light emitted from an exposure energy source, NA represents the numerical aperture of a lens and k represents a process constant. This equation teaches that, to achieve a high resolution, i.e., decrease the value of R, the wavelength of the light emitted from the exposure energy source must be shortened.
As an example, in the manufacture of semiconductor tips having a degree of integration up to 64 M bits, the i line (365 nm) of the high-pressure mercury lamp has been used as the exposure light. As positive resists for this kind of light, a number of compositions based on a novolac resin and a photo-sensitive naphthoquinonediazide have been developed, which have achieved a sufficient success in the processing of lines having widths up to about 0.3 μm. In the manufacture of semiconductor tips having a degree of integration of 256 Megabits or higher, the KrF excimer laser light (248 nm) instead of the i line has been adopted for exposure.
Further, in order to cope with the semiconductor manufacture with a degree of integration not less than 1 G bits, the use of the ArF excimer laser light (193 nm) and the F2 excimer laser light (157 nm) is under investigation for the formation of patterns finer than 0.1 μpm.
To meet such changes in the wavelength of exposure light, the composition of the resist material is also changing drastically. Since the conventional novolac resin and naphthoquinonediazide-based resist exhibits a strong absorption in the deep UV region around 248 nm, the deep UV light is difficult to reach the bottom portion of the resist, thus giving patterns having a tapered cross-section, requiring a large amount of exposure.
To solve such problems, chemically amplified resists have been developed in which a resin having a principal structure of poly(hydroxystyrene) that exhibits a weak absorption in the 248 nm region and is protected by a acid-decomposable group and a compound (photo acid generator) that generates an acid by the irradiation of a UV light are used together. Since the chemically amplified resist changes the solubility in the developer via a decomposition reaction catalyzed by the acid generated at exposed areas, it can form high-resolution patterns with a small amount of exposure.
Acid-decomposable resins and photo acid generators useful for such systems are reported in a number of papers and patents including Polym. Eng. Sci., 23, 1012 (1983), ACS. Sym., 242, 11 (1984), Macromolecules, 21, 1475 (1988), J. the Soc. of Synthet. Org. Chem., Japan, 49, 437 (1991) and Bisai Kako to Resisto (Micro-processing and Resist), published by Kyoritsu Shuppan Co., Ltd. in 1987. In the case of using the ArF excimer laser light (193 nm), the chemically amplified resists did not show satisfactory performance since compounds having an aromatic group exhibit a strong absorption at the 193 nm wavelength region.
To solve the above problem, an improvement of chemically amplified resists is being investigated by replacing the acid-decomposable resin having a basic structure of poly(hydroxystyrene) to another acid-decomposable resin in which an alicyclic structure not absorbing 193 nm light is introduced in the main or side chain of the polymer.
References can be made on such alicyclic, acid-decomposable resins to, for example, Japanese Patent Laid-Open Nos . 39665/1992, 234511/1995, 73173/1997, 199467/1995, 259626/1996, 221519/1997, 10739/1998, 230595/1997, 111569/1998, 218947/1998 and 153864/1998, and WO-97/33198.
Even the alicyclic resins proved to strongly absorb 157 nm region radiations, thus being unable to form 0.1 μm or finer patterns with use of the F2 excimer laser light (157 nm). In contrast, it has been reported in Proc. SPIE, 3678, 13 (1999) that resins to which fluorine atoms are introduced in the form of perfluoro group exhibit a sufficient transparency in the 157 nm radiation. Further, effective molecular structures of such fluorine-containing resins have been proposed in Proc. SPIE, 3999, 330, 357 and 365 (2000), and WO-00/17712.
However, the resist based on these fluorine-containing resins sometimes exhibit insufficient levels of resistance against dry etching. Moreover, due to the specific water- and oil-repelling nature originating from the perfluoro structure, the coating performance has been expected to improve to secure the uniformity of the coated surface, and the suppression of development defect has also been expected.